Ultrastructural evolution of conodont skeletal tissues - reconstruction using electron backscatter diffraction (EBSD)

• Applicant: Professor Dr. Axel Munnecke, since 9/2021
• Subject Area: Palaeontology
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 418124534

The vertebrate mineralized skeleton is among the most successful innovations in the history of life. Its properties allowed for the development of an astounding diversity of biomechanical strategies, including locomotion, food processing, predation, and body armour, stimulating major diversification episodes. The composite hydroxyapatite-organic structure of vertebrate skeletal tissues has also served as an inspiration for engineered medical materials. The understanding of the relationship between the ultrastructure and functional properties in these tissues is currently derived almost exclusively from mammal teeth. The mammalian teeth model, however, does not represent the full breadth of structures present in the earliest vertebrate hypermineralized tissues. A model linking their structure and function is needed in order to test hypotheses on their functional adaptations. This, in turn, requires a method allowing to characterise individual crystals and crystal domains quantitatively. In calcareous skeletons, this has been achieved using electron backscatter diffraction (EBSD), but attempts to employ this technique to hydroxyapatite tissues have been unsuccessful so far. We propose a research protocol allowing to apply EBSD to the earliest vertebrate hypermineralized tissues and cross-test it using in situ and powder X-ray diffraction. We focus on conodonts, a fossil group which has developed hypermineralized skeletal tissues for the first time among vertebrates and in parallel to other groups. The project aims to test the hypothesis that their hypermineralized tissues have a nanogranular composite structure. This structure has been recently demonstrated to be a common pattern in most biomineralizing animal phyla and contributes to their exceptional material properties such as resistance to crack propagation. We also test a previously proposed hypothesis that conodont crown tissues show ultrastructural adaptations to food-processing functions and the broad ultrastructural variation manifested in these adaptations is made possible through modifications of sizes and orientations of crystals and entire crystal domains at several levels of organization. Finally, we aim to assess diagenetic alteration of these patters experimentally.

• DFG Programme: Research Grants
• Major Instrumentation: EBSD Detector with a CMOS camera
• Instrumentation Group: 5140 Hilfsgeräte und Zubehör für Elektronenmikroskope
• Ehemalige Antragstellerin: Dr. Emilia Jarochowska, until 9/2021